Field of the Invention
The present invention relates generally to the field of bathymetry, and specifically to a system for creating a detailed synthetic visualization of an underwater environment.
Description of the Related Art
Current technology used for bathymetry and underwater visualization is deficient in two critical areas: sensors are incapable of high-resolution three-dimensional measurement, and software is incapable of realistically representing large, complex, dynamically changing underwater environments in real-time. As a result of these deficiencies, it has not previously been possible to develop and commercialize low-cost, high-resolution, real-time, three-dimensional underwater visualization systems.
Current State-of-the-Art Underwater Sensors:
Objects on the ocean floor that threaten navigation or national security in coastal waters, such as bottom-mounted mines, and other objects of military or commercial interest, are often obscured due to turbidity in the water column. Standard camera systems, operating passively with ambient sunlight or in combination with flood and strobe lights, can typically image through one to two optical attenuation lengths (1/k; where “k” is the diffuse attenuation coefficient).
Light is attenuated as it passes through water. That is, light gradually lessens in intensity as it passes through water (as well as other mediums, including air) as it is scattered and or absorbed. In clear water, light with the longest wavelengths are absorbed first, so red, orange, and yellow light is absorbed in shallow water than is blue and violet light. It is this fact that gives clear ocean waters a deep-blue appearance when viewed from above. Other material suspended in water, such as dirt from the bed of the body of water, chemicals, and other detritus, can drastically increase the amount of absorption and scattering of light particles and cause the light to be attenuated faster.
In the 1990s, new imaging systems based on laser illumination, (synchronous laser scan and imaging LIDAR approaches), have increased the imaging range to four to five attenuation lengths. However, light attenuation in very turbid water, such as associated with river plumes and suspended bottom sediments, render even these systems ineffective due to the limited stand-off range necessary for generating high quality imagery and the associated decrease in survey rate. Therefore, the need remains to develop compact optical systems capable of imaging through greater ranges and deployable on a variety of manned and unmanned platforms.
No low-cost, commercial, three-dimensional bathymetric LIDAR systems currently exist. However, there are a number of commercially deployed high-cost Airborne LIDAR Bathymetry (ALB) systems. ALB is an airborne survey methodology utilizing an aircraft-mounted LIDAR system to rapidly and accurately measure seabed depths and topographic elevations. These systems utilizes two wavelengths of laser light, one to measure the surface of the body of water and the other to penetrate into the body of water to measure the depth of the water.
Probably the most advanced ALB system is the SHOALS system. The SHOALS technology is owned and operated by the Joint Airborne LIDAR Bathymetry Technical Center of Expertise (JALBTCX), which is a unique partnership between the South Atlantic Division of the US Army Corps of Engineers (USACE), the Naval Meteorology and Oceanography Command/Naval Oceanographic Office, and USACE's Engineer Research and Development Center.
Although the technology is quite advanced, only a few systems exist and they are extremely expensive to own and operate. The SHOALS system utilizes very high power YAG lasers, expensive photomultiplier tubes, and stabilization systems that are intricate and expensive. These systems utilize complex algorithms to deal with surface reflection and light dispersion.
In addition to bathymetric applications, three-dimensional scanning LIDAR has recently been developed for acquiring high-density environmental ranging information on land (in air). An example of this type of system is the DeltaSphere-3000 Laser 3D Scene Digitizer being marketed by 3rdTech, Inc. This system is based on technology developed by Dr. Lars Nyland at the University of North Carolina at Chapel Hill. The system is capable of taking millions of range measurements using scanning 3D LIDAR in order to create a three-dimensional graphic image of the scanned space.
Terrain Rendering State-of-the-Art:
The state-of-the-art in visual, computer generated terrain rendering varies from simple graphics depictions created on personal computers (PC) to sophisticated, very expensive real-time simulators. In general, real-time rendering of detailed terrains poses a significant problem due to the vast amounts of data and large number of computations that are required to accurately represent complex terrain models.
On the low end of the complexity scale are graphics generated by PCs, principally used for computer gaming. Modern PCs use dedicated graphics processing units (GPU) to help offload real-time graphic rendering related work from the CPU. However, due to memory storage and computational limitations, the PC is inadequate when it comes to rendering large, highly-detailed terrain models that require a large number of polygons to accurately represent the 3D image. In an effort to overcome this problem and still maintain highly-realistic computer-generated terrains, the gaming industry has implemented a distributed computing model for delivering new and improved content to multiple clients. This content is created and processed on a centralized server, which offloads the massive storage and computational work from the PC, and is used in today's Massively Multi-player On-line Games (MMOG).
The rendering of large, detailed terrains for military simulations is accomplished using large and expensive image generator (IG) systems, such as the Harmony Military Simulator System developed by the Evans and Sutherland Company.
In addition to the hardware limitations described above, there exist significant software challenges to depicting large, moving terrains in real-time. To address some of these problems, Level of Detail (LOD) algorithms have been developed. These algorithms lower the amount of detail in terms of triangles drawn to the screen in regions which are farther away from the operator, or in areas where the number of triangles can be reduced without causing much loss in detail. By so doing, these algorithms provide high detail for objects that are in the main field of view, while limiting the overall number of triangles displayed, thereby reducing graphics-related computations. Popular LOD algorithms in use today include ROAM, SOAR, Adaptive Quadtree, and Chunking.
Although surface terrain information databases have improved as more of the world is mapped in increasing levels of detail and accuracy, underwater bathymetric databases are much further behind and for the most part remain woefully out of date. In waterways, where there are high currents such as rivers and coastal areas, the underwater landscape is in a constant state of change and not regularly measured and corrected. Furthermore, present systems do not learn about these changes and automatically update a common national or international database, nor is this information gathered from a number of geographically displaced systems and annotated for storage and redistribution.
What is needed in the art is a system that solves these problems by providing and combining new-to-the-world technologies in underwater environmental sensing and real-time underwater graphics and terrain visualization software.